php - What does setting Content-Encoding to true do? -

i've come across line in php code i've inherited:

header('content-encoding: ', true); 

looking @ mdn docs content-encoding 'true' not valid value. expecting gzip or deflate, not true.

i looked , can't see special behaviour in php if set true.

however in code looking @ line has following effect: makes file being output zipped. adds empty content-encoding header http response headers. latter understand - former not.

there interaction here use of php's ob_gzhandler() has been called , have have correctly set content-encoding header correctly gzip.

if comment out line file not zipped.

what appears happening this:

ob_gzhandler() sets content-encoding header gzip. subsequent line: header('content-encoding: ', true) - called after ob_end_clean() somehow enables prior setting - without prior setting ob_gzhandler not 'activated'. make sense?

basically - why want do:

header('content-encoding: ', true);?